1. Field of the Invention
This invention resides in materials and methods for crop protection, and is particularly concerned with soil treatments to control the growth of organisms, such as insects, fungi, and weeds, that are deleterious to crop growth.
2. Description of the Prior Art
The agricultural industry relies on effective control of insects, plant pathogens, nematodes, and weeds, for bountiful and healthy crops. One means of achieving this control is by treatment of the crops with cyanamide for both stimulation of crop growth and protection of crops from insect pests, plant pests, and fungi. Cyanamide, a term that is used to designate both hydrogen cyanamide (H2N—C≡N) and calcium cyanamide (Ca++=N—C≡N), is used particularly in Europe as an herbicide and in various parts of the world as a plant growth regulator. From its introduction in the 1950's, cyanamide has been used as a pre-emergence herbicide and a defoliant. Research has shown that the active ingredient of both hydrogen cyanamide and calcium cyanamide preparations is hydrogen cyanamide itself, with the effectiveness of calcium cyanamide being attributable at least in part to the action of moist soil on plants in hydrolyzing calcium cyanamide to hydrogen cyanamide. Hydrogen cyanamide has traditionally been applied as an aqueous liquid formulation due to the ease in which aqueous hydrogen cyanamide decomposes to urea and is then converted to ammoniacal forms of nitrogen and carbon dioxide. These metabolites serve as plant nutrients and their formation is mediated by biological organisms, physical processes, or both.
Liquid agricultural formulations suffer from certain limitations, however. In liquid cyanamide formulations, the cyanamide slowly decomposes to urea and other decomposition products, even when the formulations are kept in sealed containers. The rate of decomposition can be lessened to some degree by buffering the formulation with carboxylic acids or phosphoric acid, but not stopped entirely. Despite this, phosphoric acid has been used to some success, but in drip irrigation systems, hydrogen cyanamide formulations that contain phosphoric acid and water with a high calcium content cause plugging of the drip emitters. Plugging is also observed in spray systems that utilize spray nozzles with small diameters. Plugging can also be caused by other active ingredients and additives, upon exposure of the liquid formulation to conditions such as temperature changes and high shear stress. New additives have been developed to address this problem and to otherwise improve the formulation such as by enhancing the spreading of the active ingredient(s), but the inclusion of auxiliary chemicals in agrochemical compositions is closely regulated by the Environmental Protection Agency, and it is increasingly difficult to obtain approval of formulated compositions. In addition, the application of a liquid formulation typically requires an irrigation system, which is not available in all crop areas. Still further, while it is often desirable to combine two or more active ingredients in a single formulation for simultaneous application, certain actives are not compatible with aqueous solutions.